1. Field
The present invention relates generally to data communication, and more specifically to techniques for processing data for transmission in a time division duplexed (TDD) communication system.
2. Background
A multi-channel communication system is often deployed to provide increased transmission capacity for various types of communication such as voice, data, and so on. Such a multi-channel system may be a multiple-input multiple-output (MIMO) communication system, an orthogonal frequency division modulation (OFDM) system, a MIMO system that utilizes OFDM, or some other type of system. A MIMO system employs multiple transmit antennas and multiple receive antennas to exploit spatial multiplexing to support a number of spatial subchannels, each of which may be used to transmit data. An OFDM system effectively partitions the operating frequency band into a number of frequency subchannels (or frequency bins or subbands), each of which is associated with a respective sub-carrier on which data may be modulated. A multi-channel communication system thus supports a number of “transmission” channels, each of which may correspond to a spatial subchannel in a MIMO system, a frequency subchannel in an OFDM system, or a spatial subchannel of a frequency subchannel in a MIMO system that utilizes OFDM.
The transmission channels of a multi-channel communication system typically experience different link conditions (e.g., due to different fading and multipath effects) and may achieve different signal-to-noise-plus-interference ratios (SNRs). Consequently, the transmission capacities (i.e., the information bit rates) that may be supported by the transmission channels for a particular level of performance may be different from channel to channel. Moreover, the link conditions typically vary over time. As a result, the bit rates supported by the transmission channels also vary with time.
A time division duplexed (TDD) communication system transmits data on the forward and reverse links via the same frequency band. The forward link refers to transmission from a base station to a terminal and the reverse link refers to transmission from the terminal to the base station. In the TDD system, the transmission time is partitioned into time slots, and some of the time slots are allocated for forward link transmission and remaining time slots are allocated for reverse link transmission. Because the forward and reverse links share the same frequency band, the characteristics of the forward link may be estimated by measuring the characteristics of the reverse link, and vice versa. This reciprocity property of the forward and reverse link propagation may be used to more easily characterize the communication link.
Given the above, techniques that can be used to (1) exploit the reciprocal property of the forward and reverse links in a TDD communication system and (2) process data for transmission on multiple transmission channels with different capacities to achieve high performance are highly desirable.